Tuning fork timepiece



Oct. 11, 1966 YASUO NOMURA ET AL 3,277,644

TUNING FORK TIMEPIEGE 6 Sheets-Sheet 1 Original Filed July 1, 1963 Oct. 11, 1966 YASUQ NOMURA ETAL 3,277,644

' TUNING FORK TIMEPIECE Original Filed July 1, 1963 6 Sheets-Sheet 2 Oct. 11, 1966 YASUQ NQMURA ETAL 3,277,644

TUNING FORK TIMEPIECE Original Filed July 1, 1963 6 Sheets-Sheet 5 Oct. 11, 1966 YASUO NOMURA ETAL 3,277,644

TUNING FORK TIME'PIECE Original Filed July 1, 1963 6 Sheets-Sheet 4 Oct. 11, 1966 YASUQ NOMURA ET AL 3,277,644

TUNING FORK TIMEPIECE 6 Sheets-Sheet 5 Original Filed July 1, 1963 0m, 1966 mm MURA ETAL 3,277,644

TUNING FORK TIMEFIECIEIv Original Filed July 1, 1963 6 Sheets-Sheet 6 United States Patent 3,277,644 TUNING FORK TIMEPIECE Yasuo Nomura, Tokyo, and Hideo Iida, Koichi Iwaki, and

Shigeru Konda, Gyoda-shi, Saitama-ken, Japan, assignors to Jeco Company, Limited, Tokyo, Japan, a corporation of Japan Continuation of application Ser. No. 291,763, July 1, 1963. This application June 8, 1965, Ser. No. 471,492 6 Claims. (CI. 58-23) This application is a continuation of application Serial No. 291,763, filed July 1, 1963 and now abandoned.

This invention relates to a tuning fork clock.

Heretofore there have been clocks and watches in which balance wheels or pendulums are used as oscillators. However, such oscillators are so low in me chanical Q and isochronism that they are not satisfactory for high precision clocks. Moreover, even if it were possible to make high precision clocks with such oscillators, the manufacture of such products would be very expensive.

Tuning fork clocks and watches in which tuning forks are used instead of balance wheels and pendulums are already known, as illustrated, for example in US. Patent No. 2,971,323. However, in such tuning fork clocks, the oscillatory motion of the tuning fork is converted to rotary motion by mechanical converters which are difiicult to make and very costly.

Furthermore, a magnetic escapement mechanism has been proposed wherein a permanent magnet is attached to the forward end of an oscillator, and a rotary wheel (escapement wheel) made of a magnetic material and having magnetically nonsymmetrical undulating magnetic tracks is arranged between the magnetic poles of said permanent magnet so that said rotary wheel may be driven by the oscillatory motion of the oscillator. Such a mechanism is described, for example, in British Patent No. 660,584 but has not been practiced probably because the toque which is generated by the magnet of the oscillator attracting the nonsymmetrical part of the rotary wheel is so small that it is difiicult to synchronize both magnet and wheel. Also, it is difiicult to manufacture rotary wheels having magnetically nonsymmetrical undulated magnetic paths.

A main object of the present invention is to provide a low cost, high precision tuning fork clock wherein the oscillatory-motion of the tuning fork is converted to a rotary motion by a very simple mechanism.

Another object of the present invention is to provide easy to manufacture rotary disks having magnetically symmetrical magnetic teeth for use with a tuning fork oscillator.

A further object of the present invention is to provide a tuning fork clock having a mechanism for simply adjust- 7 ing the frequency of the mechanical oscillator.

The present invention shall now be explained with reference to the accompanying drawings of which: FIGURE 1 is a perspective view of an illustrative embodiment of the tuning fork clock according to the present invention;

FIGURE 2 is an enlarged fragmentary perspective view showing the relative positions of the magnetic poles of a magnet and a rotary disk;

FIGURE 3 is a wiring diagram for an electric reciprocating motion generating device;

FIGURES 4 to are plan views each showing the relative positions of magnetic poles and the magnetic teeth of a rotary disk;

I adjusting device.

pinion fixed to said shaft 15. -tated by a second hand gear 18 and an hour hand 22 and 3,277,644 Patented Oct. 11', 1966 In FIGURE 1, 1 is an electric reciprocating motion generating device for a tuning fork, 2 is a tuning fork having a predetermined natural frequency of vibration, 3 is a driving coil, 4 is a researching coil, 5 is a transistor, 6 is a dry cell, 7 is a resistance, 8 is a condenser and 9 and 9' are magnets.

The operation of the electric reciprocating motion generating device is as follows:

When the dry cell 6 is connected to the circuit, due to a base current flowing to the resistance 7, a collector current will flow through the driving coil 3. Due to this collector current, the driving coil 3 will attract the tuning fork 2. The researching coil 4 will research the ends of said tuning fork 2, rotary disk or whose teeth are connected only magnetically with the tuning fork 2 between the N and S poles of the magnets 11 and 11, is fixed to a shaft 13. A pinion 14 also fixed to said shaft 13 meshes with a gear 16 fixed to a shaft 15. 17 is a A second hand 20 is roa minute hand 21 are rotated through gears 19. A starting device 23 is provided for starting the clock.

An adjusting plate 24 which is so arranged that its side may be opposite the magnet 11 is fixed to one end of the shaft 25 carried in a sleeve 26. A pinion 27 fixed to the other end-of shaft 25. 28 is a spring set between the vsleeve 26 and pinion 27 to bring the tapered parts of the adjusting plate 24 and of sleeve 26 into perfectly close contact with each other. 29 is a nut to fix the sleeve 26 to a ground plate 30. 31 is a Worm gear meshed with the pinion 27. 32 is a worm gear shaft mounted in flanges 33 and 33 of plate 30. 34 is an indicating wheel fixed to the shaft 32.

In operation, when electric energy is fed to the electric reciprocating motion generating device from the electric .rotate the rotary disk 12 at a rotating speed higher than synchronized speed the oscillatory motion of the tuning fork. 2 will be transmitted as a rotary motion to the rotary disk 12 and a normal operating state will set in. That is to say, the rotary disk 12 will be rotated by the tuning fork 2 always fed with an energy to keep its oscillation by the electric reciprocating motion generating device 1 and the oscillatory motion of the tuning fork 2 will make said rotary motion perfectly synchronize. How the oscillatory motion of the tuning fork 2 is transmitted as a rotary motion to the rotary disk 12 as described above shall be more freely discussed herein with reference to FIGURES 4 to 10.

The phrase the motion of the N and S magnetic poles is used in the ensuing discussion to simplify the explanation and includes the simple oscillatory motion of the tuning fork 2 having the magnets 11 and 11' fixed to the forked ends.

In FIGURES 4 to 10, the double cross hatched member used to represent magnetic poles N and S represents the projection of the magnetic poles N and S shown in FIGURE 2 on the rotary disk 12. Furthermore, though two magnets 11 and 11 are combined with the rotary disk 12 in FIGURE 1, the operation of only one magnet is described herein but it should be apparent that the other magnet works .in the same manner.

35, 36, 37, 38 and 39 between the N and S magnetic poles will always be magnetically attracted and the rotary disk 12 will rotate either clockwise or anticlockwise by a slight angle around the center axis of the rotary disk. The parts between the adjacent outside radial magnetic teeth 35 and 41 and between the adjacent inside radial magnetic teeth 38 and 39 are punched out and generally rectangular in shape, for example, as illustrated in FIGURE 4.

Therefore, when the magnetic poles N and S further continue the motion on the track IA toward the axis 0 of the rotary disk from the position shown in FIGURE 4 (see FIGURE the rotary disk will rotate either clockwise or anticlockwise by a very small angle around the axis 0 of the rotary disk so that either the magnetic tooth 39 connected with the connecting part 36 or the magnetic tooth 38 connected with the connecting part 37 may be between the magnetic poles N and S. However, as both connecting parts 36 and 37, of the rotary disk 12 are made respectively symmetrical with respect to the radial centerline of tooth 35 OQ when the center axis OQ coincides perfectly with the track H of the magnetic poles N and S as shown in FIGURE 4, if the magnetic poles N and S move toward A on the track KAT from the magnetic tooth 35, the rotary disk 12 will rotate so that either the connecting part 36 and the tooth 39 or the connecting part 37 and the tooth 38 may happen to be guided between 13 of the rotary disk will be substantially equal to each' other in both clockwise and anticlockwise rotations and the resultant torque will be substantially equal to zero.

However, it is necessary to generate a torque on shaft 13 which is suflicient to convert the oscillatory motion of the tuning fork 2 having the magnet 11 of the .poles N and S fixed to the forked end to the rotary motion of said rotary disk 12, to rotate the rotary disk 12 in any desired direction for driving the clock mechanism and other movable parts connected to the pinion 14.

First of all, the tuning fork 2 is designed to maintain an oscillatory motion and a force to produce suflicient rotary motion above the fixed speed is applied to the rotary disk by the starting device 23. Then, when the radial magnetic tooth of the rotary disk 12 is located between the magnetic poles N and S (see FIGURE 4 or 5) and the magnetic poles N and S move toward A on the track E' from the position shown in FIGURE 4 due to the motion of the tuning fork 2, if a clockwise torque, for example, is given to the rotary disk 12 with the starting device, as shown in FIGURE 6, the rotary disk 12 will be rotated clockwise and therefore a displacement will be produced between the track E of the magnetic poles N and S and the radial centerline 6Q; of the rotary disk 12. Therefore, when the magnetic poles N and S move toward A on the track AA, the attraction received by the left magnetic tooth 38 will be so much larger than that received by the right magnetic tooth 39 that the magnetic tooth 38 will be strongly attracted by the magnetic poles N and S so as to be guided between the poles N and S and the rotary disk 12 will be rotated. Furthermore, when the magnetic tooth 38 is guided betooth 38, the magnetic tooth 41 will be strongly attracted by the magnetic poles N and S and the rotary disk 12 will rotate further clockwise so that the magnetic tooth 41 may be guided between the magnetic poles N and S. Now, when the magnetic tooth 41 is between the magnetic poles N and S, as previously explained with reference to FIGURE 6, while the magnetic poles N and S turn again to move toward A on the track AA, a displacement will be produced, the magnetic tooth 43 connected to the connecting part 42 will be attracted (see FIGURE 8) and therefore the rotary disk 12 will be rotated clockwise to guide said magnetic tooth 43 between the magnetic poles. Thus the same action will appear on all the radial centerline 0 16 6E, 0P (76 GR; 0Q etc. of the rotary disk teeth and clockwise rotation will continue. The above explanation is with regard to the case of starting the rotary disk from the position of the radial centerline of tooth 35 6Q: as in FIGURE 4. Even by starting it from the position of such radial centerline W; of tooth 38 as in FIGURE 5, the same motion will be obtained with only the phase displaced by a half cycle. In the above explanation, the rotary disk is started clockwise, however, if it is started anticlockwise, it will rotate anticlockwise. It has been explained above that the attraction is produced by the displacement between the magnetic poles N and S and the magnetic teeth 35, 38, 41 (the radially extended parts) and 43 so that the rotary disk 12 may follow the movement of the magnetic poles N and S. However, in the strict sense, the attraction may be produced also between the magnetic poles and those parts connecting the radial magnetic teeth 35, 38, 41 and 43 viz. connecting parts 36, 37, 40 and 42. Actually the attraction for connecting parts will be so much weaker that in fact, the rotary disk 12 will be practically rotated only by the attraction for the radial magnetic teeth 35, 38, 41 and 43. Therefore, if the shapes of radial magnetic teeth 35, 38, 41 and 43 are made to meet such requirements as are described herein, the shapes of the connecting parts 36, 37, 40 and 42 which are connecting said radial magnetic teeth will not be too important. For example, even if such connecting parts are formed of a nonmagnetic material, there will be no trouble in rotating the rotary disk.

In order that the oscillatory motion of the tuning fork 2 may be efiiciently and effectively converted to a rotary motion by the rotary disk 12, the shape of each of the magnetic poles N and S and the width of each of the radial magnetic teeth 35, 38, 39, 41 and 43 must be considered so that, when the radial magnetic teeth 35, 38, 39 and 41 are guided between the magnetic poles N and S, the magnetic poles N and S may attract the radial magnetic teeth strongly enough to smoothly produce a displacement between the track AA and the center axis U1 or (fi and to make the rotary disk .12 follow the movement of the magnetic poles N and S.

According to the present invention, in order to make such displacement and attraction" smoother, the width 0 of each of the magnetic poles is made smaller (or larger) than the width b of each of the magnetic teeth 35,

38, 39, 41 and 43 of the rotary disk so that the displacement may take place in a substantially unrestrained state, because, in case the width c of each of the magnetic poles N and S is made somewhat smaller than the width b of the magnetic tooth as shown in FIGURE 9, when the rotary disk 12 rotates from the position represented by the solid lines to the position represented by the dotted lines, the magnetic flux between the magnetic poles N and S will vary so little that the magnetic attraction acting on the rotary disk 12 will be able to be substantially neglected and the effect of damping such rotary motion (equal to the displacement) of the rotary disk 12 as is produced by the attraction will not be able to be considered to exist at all. In the case where the width 0 is made larger than the width b, the magnetic attraction is also considered negligible. The last case, where c equals to b is most undesirable.

The thickness d of each of the magnetic poles N and S proper to make the attraction stronger is 1.2 to 4 times as large as the width e of the connecting part. Unless the amplitude of each of the magnetic poles N and S is large enough, increasing said thickness d will impair the attraction and will not be desirable, because, if, as shown in FIGURE 10, the amplitude of each of the magnetic poles N and S is not large enough for its thickness d, such force of the lower end part of each of the magnetic poles N and S as will impart the rotation of the escapement Wheel 12 in any desired direction will act while the magnetic poles N and S move from the magnetic tooth 39 to the magnetic tooth and will impair the attraction. Therefore, said thickness d should be determined by considering not only the magnitude of the magnetic flux but also the maximum and minimum amplitudes which the forked ends of the tuning fork 2 can take.

It has been already explained that, when the tuning fork 2 is to be driven and the rotary disk 12 is to be rotated, if a torque in any desired direction is given to the rotary disk 12 by means of the starting device only at the time of starting and the escapement wheel 12 is rotated at a rotating speed higher than is fixed, the magnetic paths of the rotary disk 12 will follow the movement of the magnetic poles N and S and the rotary disk 12 will be rotated by the magnetic poles N and S.

The force to be given to the rotary disk 12 from the starting device 23qat the time of starting must be large enough to rotate said rotary disk at fixed speed.

As detailed in above, in the time keeping mechanism according to the present invention, when the oscillator (tuning fork) is oscillated by an electric or any other means, the permanent magnets fixed to the free ends will attract the'inside and outside magnetic teeth which are the main component elements of the rotary disk and the oscillatory motion of said tuning fork will be converted to the rotary motion of the rotary disk. In order that such action may take place efficiently, the width 0 of the magnetic pole is made smaller or larger than the width b of the magnetic tooth (FIGURE 9) and the thickness d of the magnetic pole is selected to be 1.2 to 4 times as large as the width e of the magnetic connecting part (FIGURE 9).

On the other hand, in the conventional mechanism of this kind or the mechanism mentioned in British Patent No. 660,584, said permanent magnets attract the undulated magnetic paths which are the main component elements of the rotary disk or escapement wheel to attain the above mentioned action. In order to make this action safe in the case that the amplitude of the oscillator is so large as to deviate from said undulated magnetic path, inside and outside magnetic paths are provided to be concave and convex so as to guide and magnet with the concave and convex parts of said undulation. Further, it is considered therein to be most desirable that the thickness of the magnetic pole (corresponding to the thickness d of the magnetic pole in the present invention) is formed to be the same as the width of the undulated magnetic path (substantially corresponding to the width b or e of the magnetic teeth in the present invention). Therefore, the magnetic parts to be attracted by the permanent magnets are the inside and the outside radial magnetic teeth of the rotary disk in the present invention but are the undulated magnetic paths in said British patent.

The pole form described in the present invention is not symmetrical or nonsymmetrical with respect to the radial magnetic teeth 38, 39, 35 and 41 (FIGURE 11).

It shall be explained with reference to FIGURE 11. For example, whether an escape wheel is symmetrical or not in a plane or in three dimensions by taking its thickness into consideration is judged with having symmetrical connecting parts to the radial axis O P in FIG. URE 11) passing through the middle point R of the two right and left sides 44 and 45 in contact with the respective adjacent connecting parts 37 and 40 from the center 0, or not.

In the present invention, a tuning fork is used as a time keeping oscillator instead of such conventional oscillator as a balance wheel or a pendulum. As the rate variation Af of the time keeping mechanism of this kind is represented by the formula wherein f is the natural frequency of the oscillator, in case a tuning fork having a value of Q of 3,000 to 5,000 much larger than of such conventional oscillators as are mentioned above is used, the rate variation A will be so small that a clock of a high precision will be obtained.

The precision of the tuning fork clock of the present invention is very high as described above. However, the precision can be further improved by providing an adjusting plate near the permanent magnet and fixed to the free end of the tuning fork.

In operation the adjusting device in the present invention varies the magnetic coupling force between the leakage flux at the forward end of a permanent magnet 11 and the adjusting plate 24.

In FIGURE 12, (A) indicating the position when the coupling force between the magnet 11 and the adjusting plate 24 is the largest and (B) indicates the case when the coupling force is the smallest. That is to say, in the present invention, the contour of the adjusting plate 24 is so determined that, when the adjusting plate 24 opposite the magnet 11 is moved from the position shown in (A) to that shown in (B) or vice versa in FIGURE 12, the relative distance between both magnetic bodies may be varied and the magnetic coupling force acting between both magnetic bodies may be controlled so that the frequency of the oscillator 2 may vary linearly with the angle of rotation of the adjusting plate 24. In or der to make the movement of the adjusting plate 24 finer and to improve the precision of the adjustment, the pinion 27 and worm gear 31 are provided so that the rotation of an indicating wheel 34 may be greatly reduced and may be transmitted to the adjusting plate 24.

As the contour of the adjusting plate 24 is so determined that the frequency of the oscillator 2 may be varied linearly with the angle of rotation of the adjusting plate 24 as described above, it is possible to equivalently vary the frequency by rotating the indicating wheel by the equivalent rotation over the entire range (that is, while the relative position between the magnet 11 and the adjusting plate 24 varies from the position shown in (A) to that shown in (B) or vice versa in FIGURE 12).

According to our experience of actually using it as an adjusting device for a tuning fork clock, when the total adjusting capacity (the amount of variation of the frequency when the adjusting plate is rotated from the position shown in (A) to that shown in (B) in FIGURE 12) is 20 seconds per day and the number of teeth of the pinion 4 is 20, 20 seconds per day can be adjusted by rotating the indicating wheel 34 by 20 revolutions, that is to say, 20 seconds per day can be correctly adjusted at a rate of one second per day per revolution.

Therefore, in the clock provided with such adjusting device, if an error of 5 seconds a day is to be corrected, the step of the clock can 'be adjusted to be substantially zero by rotating the indicating Wheel 34 by 5 revolutions in the direction in which the relative position between the adjusting plate 24 and the magnet 11 approaches the position shown in (B) in FIGURE 12 without requiring any measuring instrument.

As described above, when the frequency adjusting device according to the present invention is used, it will be possible to linearly adjust the frequency against the angle of rotation of the indicating wheel. Therefore, the present invention has a feature that the frequency of the oscillator 'can be simply and accurately adjusted to any desired value by rotating the indicating wheel an angle determined by the amount of adjustment for the unit angle of rotation of the indicating wheel and the amount of adjustment required of the oscillator without requiring any measuring instrument.

In accordance with the present invention, by effectively utilizing the attraction between the magnetic poles N and S of the magnet 11 fixed to the free end of the tuning fork 2 and the radial magnetic teeth of the rotary disk 12 combined with such loading device as the clock mechanism and the displacement between the track of the movement of the magnetic poles N and S and the center axis of the radial magnetic tooth, said rotary disk once started will be continuously rotated by the oscillatory motion of the tuning fork 2.

7 Therefore, the present invention is simple and does not include a mechanism of mechanically converting an oscillatory motion to a rotary motion as in the conventional tuning fork clock. It has therefore an effect of obtaining a tuning forkclock which is stable and trouble-free in operation and high in performance.

Furthermore, the rotary disk used in the present invention is simple in construction as well as easy to produce. The connecting magnetic parts in said rotary disk are made so narrow that, even in case the amplitude of the tuning fork is small, the oscillation of the oscillating element can be accurately caught.

We claim-as our invention:

1. In a timepiece including a rotary indicating mechanism, a support member, a tuning fork having a natural frequency of vibration with the base portion of the tuning fork being rigidly secured to said support member, a transducer operatively associated wit-h said tuning fork for vibrating the tines of said tuning fork at a predetermined frequency and an electronic control circuit responsive to the vibratory motion of said tuning fork for periodically energizing said transducer to sustain the vibratory motion of said tuning fork at said predetermined frequency, the improvement comprising:

(a) a rotary member coupled to said indicating mechanism for driving hte same;

(b) said rotary member being formed of at least two concentric circular arrays of radially extending, circumferentially spaced elements of magnetic fiux conducting material with the elements in one circle being circumferentially offset from the elements in the next adjacent circle;

(c) a permanent magnet mounted on at least one of the tines of said tuning fork including a pair of opposed pole faces of opposite polarity; and

((1) said pole faces being disposed on opposite sides of said rotary member and extending substantially parallel to the plane of said member for movement in the same direction as the vibratory motion of said tines along a radial path with respect to said rotary member so that when said tines vibrate, adjacent ones of said offset magnetic members are magnetically attracted thereby rotating said rotary members at a speed directly proportional to the frequency of vibration and independently of the amplitude of vibration of said tuning fork.

2. A timepiece in accordance with claim 1 characterized by a plurality of circumferential connecting sections interconnecting said magnetic elements and the radial width of said pole faces being substantially greater than the radial width of the circumferential connecting sections.

3. A timepiece in accordance with claim 2 wherein the radial width of the pole faces is approximately 1.2 to 4 times greater than the radial width of the connecting sections.

4. A timepiece in accordance with claim 2 wherein the circumferential width of the magnetic members is sub 'stantially less than the width of the pole faces.

'5. A timepiece in accordance with claim 2 wherein the width of the magnetic members is substantially greater than the width of the pole faces.

6. A timepiece in accordance with claim 1 including rotatable adjusting means mounted adjacent the free end of said tuning fork and said adjusting means having a surface contour so that the relative distance between said surface and said tuning fork may be varied with the magnetic coupling force acting therebetween controllably varying the frequency of the tuning fork linearly with the angle of rotation of the adjusting means.

References Cited by the Examiner UNITED STATES PATENTS 1,876,020 9/ 1932 Putnam. 1,907,531 5/1933 Fitzgerald et a1 318-310 2,571,085 10/1951 Clifford 310-103 2,606,222 8/ 1952 Clifford et a1. 2,787,115 4/ 1957 Clifford 58-116 2,946,183 7/ 1960 Clifford 58-116 2,973,619 3/1961 Clifford 58-116 3,020,425 2/ 1962 Steiner 310-20 3,171,991 3/1965 'Baumer 310-21 FOREIGN PATENTS 675,942 12/ 1963 Canada. 579,298 7/1924 France.

OTHER REFERENCES U.S.S.R. Certificate of Invention No. 131,270, filed December 22, 1959, received in U.S.P.O. Scientific Library July 26, 1961.

RICHARD B. WILKINSON, Primary Examiner.

LEO SMILOW, Examiner.

GERALD F. BAKER, Assistant Examiner. 

1. IN A TIMEPIECE INCLUDING A ROTARY INDICATING MECHANISM, A SUPPORT MEMBER, A TURNING FORK HAVING A NATURAL FREQUENCY OF VIBRATION WITH THE BASE PORTIONOF THE TUNING FORK BEING RIGIDLY SECURED TO SAID SUPPORT MEMBER, A TRANSDUCER OPERATIVELY ASSOCIATED WITH SAID TUNING FORK FOR VIBRATING THE TINES OF SAID TUNING FORK AT A PREDETERMINED FREQUENCY AND AN ELECTRONIC CONTROL CIRCUIT RESPONSIVE TO THE VIBRATORY MOTION OF SAID TUNING FORK FOR PERIODICALLY ENERGIZING SAID TRANSDUCER TO SUSTAIN THE VIBRATORY MOTION OF SAID TUNING FORK AT SAID PREDETERMINED FREQUENCY, THE IMPROVEMENT COMPRISING: (A) A ROTAYR MEMBER COUPLED TO SAID INDICATING MECHANISM FOR DRIVING THE SAME; (B) SAID ROTARY MEMBER BEING FORMED OF AT LEAST TWO CONCENTRIC CIRCULAR ARRAYS OF RADIALLY EXTENDING, CIRCUMFERENTIALLY SPACED ELEMENTS OF MAGNETIC FLUX CONDUCTING MATERIAL WITH THE ELEMENTS IN ONE CIRCLE BEING CIRCUMFERENTIALLY OFFSET FROM THE ELEMENTS IN THE NEXT ADJACENT CIRCLE; (C) A PERMANENT MAGNET MOUNTED ON AT LEAST ONE OF THE TINES OF SAID TUNING FORK INCLUDING A PAIR OF OPPOSED POLE FACES OF OPPOSITE POLARITY; AND (D) SAID POLE FACES BEING DISPOSED ON OPPOSITE SIDES OF SAID ROTARY MEMBER AND EXTENDING SUBSTANTIALLY PARALLEL TO THE PLANE OF SAID MEMBER FOR MOVEMENT IN THE SAME DIRECTION AS THE VIBRATORY MOTION OF SAID TINES ALONG A RADIAL PATH WITH REPSECT TO SAID ROTARY MEMBER SO THAT WHEN SAID TINES VIBRATE, ADJACENT ONES OF SAID OFFSET MAGNETIC MEMBERS ARE MAGNETICALLY ATTRACTED THEREBY ROTATING SAID ROTARY MEMBERS AT A SPEED DIRECTLY PROPORTIONAL TO THE FREQUENCY OF VIBRATION AND INDEPENDENTLY OF THE AMPLITUDE OF VIBRATION OF SAID TUNING FORK. 